In case of listening to audio content such as music via e.g. headphones, the surrounding noise of the listener is affecting the sonic impression of the material. The external noise may mask the perception of the music material.
When listening with headphones to audio reproduced by a music player the sound may be perfect in a listening environment with no or low external noise. In case of a noisy environment (e.g. a train) the headphone listening experience will, however, be degraded by the auditory masking effect. The low frequencies below the threshold of the external noise will not be heard well. The headphone will actually sound as if it is not supplying any frequencies below a certain low frequency. The result is a perception of a degraded bass.
Active noise control, also known as noise cancellation or active noise reduction, is a method for reducing unwanted sound by the addition of other sound that is introduced to cancel the unwanted sound. Active noise control is typically realised based on analogue circuits or digital signal processing. Adaptive algorithms are designed to analyse the waveform of the background noise. Then, a signal is generated that will either phase shift or invert the polarity of the original signal.
Noise cancellation, however, requires a special loud speaker to be collocated with the sound source to be attenuated. Still further, state of the art active noise cancelling systems degrade the lower frequency perception.
Although, there exist techniques for active noise reduction, it is generally desirable to provide alternative methods and devices for noise control.